1. Field of the Invention
This invention relates generally to an electrophotographic photosensitive member and relates more particularly to an electrophotographic photosensitive member containing an azo pigment having a particular coupler structure.
2. Description of the Prior Art
Conventionally, inorganic photoconductive materials such as selenium, cadmium sulfide and zinc oxide are generally used to form an electrophotographic photosensitive member.
An electrophotographic photosensitive member composed of organic photoconductive materials are known which include those having photoconductive polymers represented by poly N-vinylcarbazole or low molecular weight organic photoconductive materials such as 2,5-bis(p-diethylaminophenol)-1,3,4-oxadiazole, and those having combinations of these organic photoconductive materials and various kinds of dyes or pigments.
Electrophotographic photosensitive members based on the use of organic photoconductive materials are advantageous in that they can be produced with a very high productivity and at low cost because they have improved film formation properties and can be formed by coating. Also, the chromatic properties of this type of photosensitive member can be freely controlled by selecting dyestuffs or pigments to be contained. This type of photosensitive member has been widely studied because of these advantages, although the sensitivity and durability thereof are usually unsatisfactory. Recently, a function distribution type of photosensitive member has been developed which is based on lamination of a charge generation layer containing organic photoconductive dyestuffs or pigments and a charge transport layer containing a photoconductive polymer or a low molecular weight organic photoconductive material of the above mentioned type, which member is thereby remarkably improved in sensitivity and durability.
Azo pigments have superior photoconductivity and can be easily changed in various characteristics by selecting the proper combination of amino components and coupler components. Various azo pigment compounds have, therefore, been proposed including the ones that are disclosed in Japanese Patent Laid Open Nos.56 1944, 56-5553, and 56-150751 which relate to the present invention.
However, the properties of conventional electrophotographic photosensitive members having azo pigments are unsatisfactory in terms of sensitivity or potential stability during repeated use. Accordingly, there are few conventional photosensitive members which have been put to practical use.